High frequency filter for improved RF bias signal stability

ABSTRACT

A plasma-assisted etch process for the manufacture of semiconductor or MEMS devices employs an RF source to generate a plasma that is terminated through an electrode. The termination is designed as a “short” at the frequency of the RF source to minimize voltage fluctuations on the electrode due to the RF source energy. The electrode voltage potential can then be accurately controlled with a bias source, resulting in improved control of etch depth of a semiconductor substrate disposed on the electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Provisional Application No.61/674,163, filed Jul. 20, 2012, titled “HIGH FREQUENCY FILTER FORIMPROVED RF BIAS SIGNAL STABILITY”, which is hereby incorporated byreference in its entirety.

BACKGROUND

Semiconductor and micro electro mechanical systems (MEMS) devicesrequire myriad manufacturing processes to form the required complexelectrical and mechanical structures. These devices are continuallybeing reduced in size, resulting in associated tighter manufacturingprocess tolerances. One such manufacturing process employed is aplasma-assisted etch process.

Manufacturing variables of an etch process may result in a broadstatistical distribution for the dimensions of the structures formedwithin a group of wafers being etched. Moreover, variability in themanufacturing process can also cause statistical distributions instructural dimensions within a single wafer. Such variations may be toogreat to enable efficient production of the devices.

For example, during the manufacture of semiconductor or MEMS devices,trenches are often etched into substrate materials. Although it is oftendesirable to etch trenches that have a uniform depth across the waferand do not vary from wafer to wafer, it may be difficult to etch suchstructures.

SUMMARY

The terms “invention,” “the invention,” “this invention” and “thepresent invention” used in this patent are intended to refer broadly toall of the subject matter of this patent and the patent claims below.Statements containing these terms should not be understood to limit thesubject matter described herein or to limit the meaning or scope of thepatent claims below. Embodiments of the invention covered by this patentare defined by the claims below, not this summary. This summary is ahigh-level overview of various aspects of the invention and introducessome of the concepts that are further described in the DetailedDescription section below. This summary is not intended to identify keyor essential features of the claimed subject matter, nor is it intendedto be used in isolation to determine the scope of the claimed subjectmatter. The subject matter should be understood by reference to theentire specification of this patent, all drawings and each claim.

Embodiments of the invention include plasma etching and/or depositionsystems having a Radio Frequency (RF) power delivery system designed todeliver RF source energy so that it that forms a plasma within aprocessing chamber. The RF source energy may be configured to beterminated to ground through an electrode disposed within the processingchamber. A bias drive source may apply a bias to the electrode tocontrol the directionality of the ions from the plasma such that itallows control of dimensions and anisotropy of etched features. A filtermay be disposed between the bias drive source and the electrode, andconfigured to pass bias energy to the electrode and block RF sourceenergy from reaching the bias drive source. In some embodiments thefilter may also house an RF source termination. The RF sourcetermination may be configured to provide a designed terminationimpedance. In a preferred embodiment, for example, to act as a very lowimpedance path, sometimes referred to as a ‘short’ at the frequency ofthe RF source.

These illustrative embodiments are mentioned not to limit or define thedisclosure, but to provide examples to aid understanding thereof.Additional embodiments are discussed in the Detailed Description, andfurther description is provided there. Advantages offered by one or moreof the various embodiments may be further understood by examining thisspecification or by practicing one or more embodiments presented.

BRIEF DESCRIPTION OF THE FIGURES

These and other features, aspects, and advantages of the presentdisclosure are better understood when the following Detailed Descriptionis read with reference to the accompanying drawings.

Illustrative embodiments of the present invention are described indetail below with reference to the following drawing figures:

FIG. 1 depicts a sectional view of an example of an etch reactor inaccordance with some embodiments of the present invention.

FIG. 2 depicts a functional schematic of an example of a plasma etchsystem in accordance with some embodiments of the present invention.

FIG. 3 shows a graph illustrating the variation in etch depth of wafersin accordance with some embodiments of the invention.

FIG. 4 shows an example of a filter according to some embodiments of theinvention.

FIG. 5 shows an example of a filter disposed between a match and anelectrode according to some embodiments of the invention.

FIG. 6 shows an example of a filter disposed between a match and anelectrode according to some embodiments of the invention.

FIG. 7 shows an example of a system with two filters according to someembodiments of the invention.

DETAILED DESCRIPTION

The subject matter of embodiments of the present invention is describedhere with specificity to meet statutory requirements, but thisdescription is not necessarily intended to limit the scope of theclaims. The claimed subject matter may be embodied in other ways, mayinclude different elements or steps, and may be used in conjunction withother existing or future technologies. This description should not beinterpreted as implying any particular order or arrangement among orbetween various steps or elements except when the order of individualsteps or arrangement of elements is explicitly described.

FIG. 1 depicts a sectional view of an example of an etch reactor 100 inaccordance with some embodiments of the present invention. Etch reactor100 uses radio frequency (RF) power from RF source 114 to create aplasma 170 that operates on a substrate (e.g., a silicon wafer) 150.Substrate 150 is placed on an electrode which incorporates anelectrostatic chuck 142. The electrode acts as a ground return path forRF source 114 energy. A separate frequency from a bias power source 156may be used to apply bias power to the lower electrode to increase theetch rate and anisotropy of etch reactor 100, as discussed in moredetail below.

Several problems may arise when one frequency is used to power plasma170 and another frequency is used to apply a bias voltage to theelectrode. The combination of the RF source energy and the bias energymay result in an inconsistent voltage potential on the electrode. Thisinconsistent voltage potential on the electrode may result ininconsistent acceleration of ions from plasma 170 into substrate 150,increasing the variation in etch depth of substrate 150. Morespecifically, if the impedance of electrode 140 to ground is left tochance, then the stability of the voltages at the electrode surface maybe unrepeatable and the etch depth of substrate 150 may be inconsistent,as will be shown in more detail below. Additionally, if there is a biaspower source 156 control circuit that is affected by the source energy,it can interfere with precise metering and control of the bias drivesource. More specifically, in some embodiments, bias drive 156 controlcircuitry may be “contaminated” by the source frequency resulting in anincreased variation in etch depth.

In some embodiments, a termination having a designed impedance to groundmay be coupled to the electrode. In further embodiments, the terminationmay be designed as a “short” at the frequency of RF source 114 tominimize voltage fluctuations of the electrode due to the RF sourceenergy. In some embodiments a filter 137 may be disposed between theelectrode and bias power source 156. Filter 137 may be used to block RFsource 114 energy from reaching bias power source 156 while allowingenergy from the bias power source to reach the electrode. In anembodiment, filter 137 may also house and/or be integrated with thetermination. These and other aspects of filter 137 will be described inmore detail below.

Etch reactor 100 includes a lower chamber body 102, an upper chamberbody 104, and a ceiling 106 which enclose a process volume 108. Ceiling106 may be flat or have other geometry. In one embodiment, ceiling 106is a dome. An interchangeable spacer 110 is provided between ceiling 106and upper chamber body 104 so that the inclination and/or height ofceiling 106 relative to upper chamber body 104 may be selectivelychanged as desired.

An RF coil 112 is disposed above ceiling 106 and coupled to RF source114 through a matching circuit 116. Ceiling 106 is transmissive to theRF power such that RF source power applied to RF coil 112 from RF source114 may be inductively coupled to and energize gases disposed in aprocess volume 108 of reactor 100 to maintain a plasma 170.

The source power may be provided at a radio frequency within a rangefrom about 2 MHz to about 60 MHz at a power within a range from about 10watts to about 5000 watts. The source power may be pulsed. In someembodiments the source power is applied at a frequency of 13.56 MHz.Other frequencies and powers may be employed without departing from theinvention.

The upper chamber body 104 includes a pumping channel 118 that connectsprocess volume 108 of reactor 100 to a pump 120 through a throttle valve122. Pump 120 and throttle valve 122 may be operated to control thepressure within process volume 108 of reactor 100. Pump 120 also removesetch by-products. A baffle plate 180 may be disposed in pumping channel118 to minimize contamination of pump 120 and to improve conductancewithin process volume 108.

Etch reactor 100 may have a fast gas exchange system 124 coupled theretothat provides process and/or other gases to process volume 108 throughnozzles 126 positioned around the interior of upper chamber body 104 orother suitable location. Fast gas exchange system 124 selectively allowsany singular gas or combination of gases to be provided to processvolume 108. In some embodiments, fast gas exchange system 124 has fourdelivery lines 128, each coupled to a different gas source. Deliverylines 128 may be coupled to the same or different nozzles 126.

In the embodiment depicted in FIG. 1, each delivery line 128 includes afirst valve 130, a mass flow meter 132, and a second valve 134. Secondvalves 134 are coupled to a common tee 138, which is coupled to nozzles126. The conduits through which gases flow from mass flow meters 132 toprocess volume 108 may be less than about 2.5 m in length, therebyallowing faster switching times between gases. Fast gas exchange system124 may be isolated from process volume 108 of etch reactor 100 by anisolation valve 136 disposed between tee 138 and nozzles 126.

An exhaust conduit 162 may be coupled between isolation valve 136 andtee 138 to allow residual gases to be purged from fast gas exchangesystem 124 without entering etch reactor 100. A shut off valve 164 isprovided to close exhaust conduit 162 when gases are delivered toprocess volume 108 of etch reactor 100.

The gas sources coupled to fast gas exchange system 124 may providegases, including but not limited to, sulfur hexafluoride (SF₆), oxygen(O₂), argon (Ar), trifluoromethane (CHF₃), octafluorocyclobutane (C₄F₈),nitrogen trifluoride (NF₃), carbon tetrafluoride (CF₄), trifluoromethane(CHF₃), chlorine trifluoride (CIF₃), bromine trifluoride (BrF₃), iodinetrifluoride (IF₃), a helium-oxygen gas mixture (He:O₂), ahelium-hydrogen gas mixture (He:H₂), hydrogen (H₂), helium (He), and/orother gases for use in the processes as described herein. The flowcontrol valves may include pneumatic operation to allow rapid response.In one example, fast gas exchange system 124 is operable to deliver SF₆and C₄F₈ at up to about 1000 sccm, helium at about 500 sccm, and oxygen(O₂) and argon at about 200 sccm. In an alternative embodiment, fast gasexchange system 124 may further include a third gas panel comprising ofa plasma sustaining gas, such as argon and/or He, and operable tocontinuously deliver the gas to etch reactor 100 during the cyclicaletching method described further below.

Etch reactor 100 may additionally include a substrate support assembly140 disposed in process volume 108. Substrate support assembly 140includes an electrostatic chuck 142 mounted on a thermal isolator 144.Thermal isolator 144 insulates electrostatic chuck 142 from a stem 173that supports electrostatic chuck 142 above the bottom of lower chamberbody 102.

Lift pins 146 are disposed through substrate support assembly 140. Alift plate 148 is disposed below substrate support assembly 140 and maybe actuated by a lift 154 to selectively displace lift pins 146 to liftand/or place a substrate 150 on an upper surface 152 of electrostaticchuck 142.

Electrostatic chuck 142 includes at least one electrode (the bottomelectrode) which may be energized to electrostatically retain substrate150 to upper surface 152 of electrostatic chuck 142. An electrode ofelectrostatic chuck 142 is coupled to bias power source 156 through amatching circuit 158. Bias power source 156 may selectively energize theelectrode of electrostatic chuck 142 to control the directionality ofplasma 170 ions during etching.

The bias power applied to electrostatic chuck 142 by bias power source156 may be pulsed, e.g. repeatedly storing or collecting the energy overa time period and then rapidly releasing the energy over another timeperiod to deliver an increased instantaneous amount of power, while thesource power may be continuously applied. In particular, the bias powermay be pulsed using generator pulsing capability set by a control systemto provide a percentage of time that the power is on, which is referredto as the duty cycle. In one embodiment, the time on and the time off ofa pulsed bias power may be uniform throughout the etching cycles. Forexample, if the power is on for about 3 msec and off for about 15 msec,then the duty cycle would be about 16.67%. The pulsing frequency incycles per second or hertz (Hz) is equal to 1.0 divided by the sum ofthe on and off time periods in seconds. For example, when the bias poweris on for about 3 msec and off for about 15 msec, for a total of about18 msec, then the pulsing frequency in cycles per second is about 55.55Hz. In one embodiment, a specialized pulsing profile where the on/offtiming changes during the etching cycles may be used. In one embodiment,by changing the bias power applied to the substrate, the etching cyclemay switch between the deposition and/or etching steps. The bias poweris pulsed to help reduce scalloping of the trench sidewalls (improveanisotropy), improve resist selectivity, improve the etch rate, andprevent material interface notching.

The bias power may be provided within a range from DC to about 1 MHz ata power within a range from about 1 watt to about 5000 watts. In someembodiments the bias power is applied at a frequency of 400 kHz. Otherfrequencies and powers may be employed without departing from theinvention.

In some embodiments a backside gas source 160 may be coupled throughsubstrate support assembly 140 to provide one or more gases to a spacedefined between substrate 150 and upper surface 152 of electrostaticchuck 142. Gases provided by backside gas source 160 may include Heand/or a backside process gas. The backside process gas is a gasdelivered from between the substrate and the substrate support whichaffects the rate of etch or polymerization during the etch cycle byreacting with the materials in the chamber, such as process gases, etchby-products, mask or other layers disposed on the substrate or thematerial targeted for etching. In some embodiments, the backside processgas is an oxygen containing gas, such as O₂. In some embodiments, aratio of He to O₂ in the backside gas is about 50:50 to about 70:30 byvolume or by mass for silicon etch applications. It is contemplated thatother backside process gases may be utilized to control the processesnear the edge of the substrate. The use of backside process gases may beused beneficially for single step etch processes as well as cyclicaletch processes.

To enable the process gas provided by backside gas source 160 to reachthe edge of substrate 150, the rate of backside gas leakage from underthe edge of substrate 150 may be higher than that of conventionalbackside gas systems. In some embodiments, the leak rate may be elevatedby maintaining the pressure of the gases in a space between substrate150 and upper surface 152 of electrostatic chuck 142 between about 4 and26 Torr. In some embodiments, the pressure may be maintained betweenabout 10 and 22 Torr. In some embodiments, the pressure may bemaintained between about 14 and 20 Torr. The leak rate may also beachieved by providing notches or other features in a lip supportingsubstrate 150 and upper surface 152 of electrostatic chuck 142 whichpromotes leakage of the backside gas between electrostatic chuck 142 andsubstrate 150.

Further as shown in FIG. 1, etch reactor 100 may include a controller171 which generally comprises a central processing unit (CPU) 172, amemory 174, and support circuits 176 and is coupled to and controls etchreactor 100 and various system components, such as RF source 114, biassource 156, fast gas exchange system 124 and the like, directly (asshown in FIG. 1) or, alternatively, via other computers or controllers(not shown) associated with the process chamber and/or the supportsystems. Controller 171 may be one of any form of general-purposecomputer processor that can be used in an industrial setting forcontrolling various chambers and sub-processors. Memory, orcomputer-readable medium, 174 of CPU 172 may be one or more of readilyavailable memory such as random access memory (RAM), read only memory(ROM), floppy disk, hard disk, or any other form of digital storage,local or remote. Support circuits 176 are coupled to CPU 172 forsupporting the processor in a conventional manner. These circuitsinclude cache, power supplies, clock circuits, input/output circuitryand subsystems, and the like. Myriad processes may be stored in memory174 as software routines. The software routine, when executed by the CPU172, transforms the general purpose computer into a specific purposecomputer (controller) 178 that controls the operation of etch reactor100. The software routine may also be stored and/or executed by a secondCPU (not shown) that is remotely located from the hardware beingcontrolled by CPU 172 of controller 174. Other configurations of etchreactor 100 are known to those of skill in the art, are within the scopeof this disclosure and may be employed in other embodiments.

A functional schematic of a plasma etch system 200 in accordance withembodiments of the invention is shown in FIG. 2. FIG. 2 is forillustrative purposes and other frequencies and circuit architecturesmay be employed without departing from the invention. An RF source 205operating at 13.56 MHz powers an RF induction coil 220 through an RFmatching circuit 210. As defined herein, matching, matching circuits andimpedance matching shall mean that the real part of the impedance shouldbe approximately equal to the real part of the load and reactance'sshould be approximately equal and opposite in character. In someembodiments, RF source 205 may operate in a delivered power mode where acontrol system maintains a constant level of delivered power to RFinduction coil 220. Delivered power is equal to the measured forwardpower (power from RF source 205) minus the measured reflected power. Inother embodiments, RF source 205 may operate in a forward power modewhere reflected power is not compensated for.

RF source 205 is coupled to RF matching circuit 210 and RF inductioncoil 220 by RF conduit 215. The path of the 13.56 MHz RF source 205energy is shown with a dashed line for clarity. Induction coil 220generates a plasma 225 within chamber 230. RF matching circuit 210corrects the electromagnetic match of induction coil 220 to that of RFsource 205 to maximize power transfer from the RF source to the RFinduction coil. RF source 205 energy is then coupled from plasma 225 toelectrode 235 through RF source ground path 240 in filter 137. In someembodiments RF matching circuit 210 is variable and dynamically changesimpedance to compensate for changes in plasma 225 impedance. In otherembodiments, RF matching circuit 210 is fixed and the frequency of RFsource 205 may be varied to compensate for changes in plasma 225impedance. In such embodiments the impedance of the fixed RF matchingcircuit 210 may change with frequency. RF drive 205 output frequency maybe either statically or dynamically altered to improve impedancematching.

A bias drive source 260 operating at 400 kHz applies a bias to electrode235 through a bias drive matching circuit 265 and filter 137. Bias drivesource 260 applies electromagnetic energy to electrode 235 to accelerateions from plasma 225 into substrate 150 (see FIG. 1) to increase theetch rate of substrate 150 (see FIG. 1) and increase etch anisotropy.Thus the voltage potential of electrode 235 affects both the rate ofetch and feature attributes of substrate 150. In some embodiments, biassource 260 may operate in a delivered power mode where a control systemmaintains a constant level of delivered power to electrode 235.Delivered power is equal to the measured forward power (power from biassource 260) minus the measured reflected power. In other embodiments,bias source 260 may operate in a forward power mode where reflectedpower is not compensated for.

Bias conduit 270 connects bias source 260 to bias matching circuit 265,filter 137 and electrode 235. The path of the 400 kHz energy is shownwith a solid line for clarity. In embodiments where bias drive source260 uses RF energy, bias matching circuit 265 transforms theelectromagnetic impedance of electrode 235 to equal or close to thedesigned output impedance of bias drive source 260 to maximize powertransfer from the bias source to the electrode. In some embodiments biasmatching circuit 265 is variable and dynamically changes impedance tocompensate for changes in impedance. In other embodiments, bias matchingcircuit 265 is fixed and the frequency of bias source 260 may be variedto compensate for changes in impedance. In such embodiments theimpedance of the fixed bias matching circuit 265 may change withfrequency. Bias drive 260 output frequency may be either statically ordynamically altered to improve impedance matching. In some embodiments,an RF sensor 290 is connected to electrode 235 and used to control biasdrive source 260 or provide open-loop monitoring of applied power. Infurther embodiments, RF sensor 290 may be housed with filter 137. Insome embodiments, bias matching circuit 265 may be housed with filter137 and optional RF sensor 290.

To sustain a plasma, a closed loop circuit from RF source 205, throughplasma 225, through substrate 150, through electrode 235, throughtermination 250 to ground and back to the RF source is used. Thus,termination 250 terminates RF source 205 energy to ground. In someembodiments, termination 250 is designed to minimize voltagefluctuations in electrode 235 by “shorting” the 13.56 MHz RF source 205energy to ground by providing a designed low impedance path to minimizevoltage at the electrode surface. This “short” may serve to sufficientlyattenuate voltage fluctuations on electrode 235 due to RF source 205energy such that the voltage potential of electrode 235 may beaccurately and consistently controlled with bias drive source 260. Theimproved accuracy and consistency of control of voltage on electrode 235may provide improved consistency and uniformity of the etch rate ofsubstrate 150 of etch system 200. Other embodiments of termination 250may be designed to be an “open” or a “load”, or other terminationimpedance at the frequency of RF source 205. The RF power circuit may bedesigned considering, but not limited to, RF matching network 210, RFconduit 215, RF induction coil 220, plasma 225, electrode 235 andtermination 250. The design may be performed using electromagneticlumped element or full-field solver simulation tools. Common tools forsuch implementations are PSPICE from Cadence Incorporated and HFSS fromAnsys Incorporated. In some embodiments termination 250 may not behoused with filter 137.

In further embodiments that employ RF sensor 290 to control bias drivesource 260, the reduced voltage fluctuation of electrode 235 due to the“shorted” RF source 205 energy may result in increased accuracy andrepeatability of the RF sensor. The improved accuracy and repeatabilitymay enable bias drive 260 to apply a more consistent and repeatable biasto electrode 235, resulting in improved consistency and uniformity ofthe etch rate of substrate 150 of etch system 200. In other embodiments,RF sensor 290 may not be used to control bias drive source 260, or mayhave a selective response that only responds to RF source 205 energy.

In some embodiments, filter 137 may be configured to perform one or morefunctions related to RF source 205 and/or bias drive source 260. Filter137 may use blocking circuit 285 to perform the function of blocking the13.56 MHz RF source energy from being coupled from electrode 235 to biasdrive source 260 through bias conduit 270. In still further embodiments,filter 137 may also be configured to allow bias drive source 260 energyto pass through to electrode 235, using, for example, filtering circuit280. In some embodiments, a low pass filter may be used to perform theblocking and passing functions, while in other embodiments a band passor other filter may be used. In further embodiments, filter 137 may beintegrated including the functions of blocking, passing and terminatingwhile in other embodiments filter 137 may be componentized wherein eachfunction is performed independently. In other embodiments, bias matchingcircuit 265 may be integrated with filter 137. The frequencies employedin etch system 200 are for example only, other and additionalfrequencies including a DC bias may be employed without departing fromthe invention.

The graph illustrated in FIG. 3 shows the effect of filter 137 in someembodiments. The first three wafers 305 and the last four wafers 310were performed without using filter 137. These wafers show the largenon-uniformity in etch depth, which ranges from approximately 1% to 5%.For some products, this non-uniformity is unacceptable for production.Embodiments of the invention reduce the variation in etch depth as shownin middle wafers 315. The variation in middle wafers 315 ranges fromapproximately 2% to 3%, demonstrating an improvement in consistency ofetch depth.

FIG. 4 shows an example of filter 137 used in some embodiments. Otherconfigurations of filter 137 may be employed and are within the scope ofthis disclosure. Filter 137 can be coupled in series (or inline) betweenelectrode 235 (see FIG. 2) and bias power source 260. Filter 137 mayperform blocking, passing, termination and sensing functions for etchsystem 200 (see FIG. 2). As illustrated, in this embodiment, filter 137includes inductor 415, first capacitor 410, and second capacitor 420.Inductor 415 may be disposed between first capacitor 410 and secondcapacitor 420. First capacitor 410 and second capacitor 420 may beconnected to ground. In one embodiment, inductor 415 may have a value ofapproximately 4 microhenries, first capacitor 410 may have a value ofapproximately 1200 picofarads and second capacitor 420 may have a valuebetween approximately 150 to 200 picofarads. In some embodiments, secondcapacitor 420 may be matched to the impedance of bias conduit 270 thatconnects to electrode 235 (see FIG. 2), which may depend on the lengthof the bias conduit.

In some embodiments, RF sensor 405 may also be included in series withfilter 137 and may or may not be housed with filter 137. RF sensor 405may provide feedback to bias drive source 260 (see FIG. 2) to manageelectrode 235 voltage and the rate of etch of substrate 150 (see FIG.1). In some embodiments bias conduit 270 may be coupled directly tofilter 137, for example, without a removable connector. The design andselection of components for filter 137 may vary depending, for example,on the type of deposition or etch system, RF source 205 frequency, RFsource 205 impedance, RF matching circuit 210 characteristics, RFconduit 215, plasma 225 characteristics, electrode 235 impedance, biaspower source 260 impedance, bias matching circuit 265 characteristics,bias conduit 270 characteristics and the characteristics of the othercomponents contained in filter 137. The values and configuration of theelectrical components within filter 137 may be changed and suchalterations are within the scope of this disclosure.

For example, in some embodiments, filter 137 may be designed to have a 3DB cutoff frequency of approximately 4.2 MHz, passing energy at 400 kHzand attenuating energy at 13.56 MHz. In other embodiments, inductor 415may have a value of 3.79 microhenries, first capacitor may have a valueof 757.9 picofarads and second capacitor may have a value of 757.9picofarads. In further embodiments filter 137 can be designed with anincreased number of poles to change the slope of the attenuation curve.In some embodiments filter 137 may be designed to be a single pole, atwo pole, a three pole or other configuration of a low pass filter. Infurther embodiments, filter 137 may be designed to be a bandpass filter.In other embodiments of filter 137, termination impedance 250 (see FIG.2) to ground for RF source energy can be designed to be a matched short,a matched open, a matched load or anything in between. Termination 250design can be used to manage electrode 235 (see FIG. 2) voltage andcurrent. In some embodiments termination 250 impedance to ground isdesigned to minimize the voltage fluctuation of electrode 235.Embodiments of the invention may also improve bias source 260 (see FIG.2) voltage signal quality and/or dampen any interference from other RFfrequencies (e.g., RF source 205 frequency). Myriad configurations offilter 137 are within the scope of this disclosure.

In some embodiments, filter 137 can be housed within an enclosure andplaced near electrode 235. The enclosure can be constructed to protectthe electrical components from the harsh deposition and/or etchingenvironment that may be found within the chamber.

FIG. 5 shows another example of filter 137 coupled with an RF source andchamber 515. Filter 137 can be coupled with match circuit 505 using aconnector 525. In the figure, an example connector is shown as a quickdisconnect coaxial connector. Match circuit 505 can be used to match theimpedance of electrode 510. Filter 137 is coupled with electrode 510using cable 520. Electrode 510 is then coupled with RF source andchamber 515.

FIG. 6 shows yet another example of filter 137 coupled with an RF sourceand chamber 615. Filter 137 can be coupled with match circuit 605 andelectrode 610 with cable 620 and cable 621, respectively. As shown inFIGS. 6 and 7, filter 137 can be placed between match circuit 605 andelectrode 610 in different of configurations. Various otherconfigurations may be used, including positions between bias source andelectrode.

FIG. 7 shows an example of a system with two separate filters accordingto some embodiments of the invention. This embodiment can be used for anumber of different reasons such as, for example, to filter out two ormore frequencies. RF source 735 may apply power to reactor chamber 725through RF source matching network 730. First source filter 705 can becoupled with an electrode in chamber 725 and match circuit 715, which iscoupled with RF bias generator 720. Second filter 710 can be coupledwith ground and reactor chamber 725 through the electrical channelbetween first filter 705 and chamber 725. This system can be used, forexample to attenuate more than one source frequency. In some embodimentsboth first filter 705 and second filter 710 can be disposed within thesame housing. In other embodiments, second filter 710 may be a matchedimpedance termination for source 735.

Embodiments of the invention can be used with multi frequency MEMS etchconfigurations. In some embodiments a low pass filter or a first sourcefrequency filter can be used. Some embodiments can used inmulti-frequency plasma processing apparatus (i.e. for CVD, or etchsystems). In some embodiments the source and Bias frequency combinationsdo not have to be strictly similar to MEMS etch configuration (i.e.13.56 MHz source, and 400 KHz Bias). In some embodiments a combinationof any other two frequencies can be applicable using one filer (i.e.LPF/First Source Frequency Filter).

Different arrangements of the components depicted in the drawings ordescribed above, as well as components and steps not shown or describedare possible. Similarly, some features and subcombinations are usefuland may be employed without reference to other features andsubcombinations. Embodiments of the invention have been described forillustrative and not restrictive purposes, and alternative embodimentswill become apparent to readers of this patent. Accordingly, the presentinvention is not limited to the embodiments described above or depictedin the drawings, and various embodiments and modifications can be madewithout departing from the scope of the claims below.

A computational system can be used to perform any of the embodiments ofthe invention. For example, the computational system can be used toexecute methods and/or processes that control etch depth. As anotherexample, the computational system can be used perform any calculation,identification and/or determination described here. The computationalsystem includes hardware elements that can be electrically coupled via abus (or may otherwise be in communication, as appropriate). The hardwareelements can include one or more processors, including withoutlimitation one or more general-purpose processors and/or one or morespecial-purpose processors (such as digital signal processing chips,graphics acceleration chips, and/or the like); one or more inputdevices, which can include without limitation a mouse, a keyboard and/orthe like; and one or more output devices, which can include withoutlimitation a display device, a printer and/or the like.

The computational system may further include (and/or be in communicationwith) one or more storage devices, which can include, withoutlimitation, local and/or network accessible storage and/or can include,without limitation, a disk drive, a drive array, an optical storagedevice, a solid-state storage device, such as a random access memory(“RAM”) and/or a read-only memory (“ROM”), which can be programmable,flash-updateable and/or the like. The computational system might alsoinclude a communications subsystem, which can include without limitationa modem, a network card (wireless or wired), an infrared communicationdevice, a wireless communication device and/or chipset (such as aBluetooth device, an 802.6 device, a WiFi device, a WiMax device,cellular communication facilities, etc.), and/or the like. Thecommunications subsystem may permit data to be exchanged with a network(such as the network described below, to name one example), and/or anyother devices described herein. In many embodiments, the computationalsystem will further include a working memory, which can include a RAM orROM device, as described above.

The computational system also can include software elements, shown asbeing currently located within the working memory, including anoperating system and/or other code, such as one or more applicationprograms, which may include computer programs of the invention, and/ormay be designed to implement methods of the invention and/or configuresystems of the invention, as described herein. For example, one or moreprocedures described with respect to the method(s) discussed above mightbe implemented as code and/or instructions executable by a computer(and/or a processor within a computer). A set of these instructionsand/or codes might be stored on a computer-readable storage medium, suchas the storage device(s) described above.

In some cases, the storage medium might be incorporated within thecomputational system or in communication with the computational system.In other embodiments, the storage medium might be separate from acomputational system (e.g., a removable medium, such as a compact disc,etc.), and/or provided in an installation package, such that the storagemedium can be used to program a general purpose computer with theinstructions/code stored thereon. These instructions might take the formof executable code, which is executable by the computational systemand/or might take the form of source and/or installable code, which,upon compilation and/or installation on the computational system (e.g.,using any of a variety of generally available compilers, installationprograms, compression/decompression utilities, etc.) then takes the formof executable code.

Numerous specific details are set forth herein to provide a thoroughunderstanding of the claimed subject matter. However, those skilled inthe art will understand that the claimed subject matter may be practicedwithout these specific details. In other instances, methods, apparatusesor systems that would be known by one of ordinary skill have not beendescribed in detail so as not to obscure claimed subject matter.

Some portions are presented in terms of algorithms or symbolicrepresentations of operations on data bits or binary digital signalsstored within a computing system memory, such as a computer memory.These algorithmic descriptions or representations are examples oftechniques used by those of ordinary skill in the data processing artsto convey the substance of their work to others skilled in the art. Analgorithm is a self-consistent sequence of operations or similarprocessing leading to a desired result. In this context, operations orprocessing involves physical manipulation of physical quantities.Typically, although not necessarily, such quantities may take the formof electrical or magnetic signals capable of being stored, transferred,combined, compared or otherwise manipulated. It has proven convenient attimes, principally for reasons of common usage, to refer to such signalsas bits, data, values, elements, symbols, characters, terms, numbers,numerals or the like. It should be understood, however, that all ofthese and similar terms are to be associated with appropriate physicalquantities and are merely convenient labels. Unless specifically statedotherwise, it is appreciated that throughout this specificationdiscussions utilizing terms such as “processing,” “computing,”“calculating,” “determining,” and “identifying” or the like refer toactions or processes of a computing device, such as one or morecomputers or a similar electronic computing device or devices, thatmanipulate or transform data represented as physical electronic ormagnetic quantities within memories, registers, or other informationstorage devices, transmission devices, or display devices of thecomputing platform.

The system or systems discussed herein are not limited to any particularhardware architecture or configuration. A computing device can includeany suitable arrangement of components that provides a resultconditioned on one or more inputs. Suitable computing devices includemultipurpose microprocessor-based computer systems accessing storedsoftware that programs or configures the computing system from a generalpurpose computing apparatus to a specialized computing apparatusimplementing one or more embodiments of the present subject matter. Anysuitable programming, scripting, or other type of language orcombinations of languages may be used to implement the teachingscontained herein in software to be used in programming or configuring acomputing device.

Embodiments of the methods disclosed herein may be performed in theoperation of such computing devices. The order of the blocks presentedin the examples above can be varied—for example, blocks can bere-ordered, combined, and/or broken into sub-blocks. Certain blocks orprocesses can be performed in parallel.

The use of “adapted to” or “configured to” herein is meant as open andinclusive language that does not foreclose devices adapted to orconfigured to perform additional tasks or steps. Additionally, the useof “based on” is meant to be open and inclusive, in that a process,step, calculation, or other action “based on” one or more recitedconditions or values may, in practice, be based on additional conditionsor values beyond those recited. Headings, lists, and numbering includedherein are for ease of explanation only and are not meant to belimiting.

While the present subject matter has been described in detail withrespect to specific embodiments thereof, it will be appreciated thatthose skilled in the art, upon attaining an understanding of theforegoing, may readily produce alterations to, variations of, andequivalents to such embodiments. Accordingly, it should be understoodthat the present disclosure has been presented for purposes of examplerather than limitation, and does not preclude inclusion of suchmodifications, variations and/or additions to the present subject matteras would be readily apparent to one of ordinary skill in the art.

That which is claimed:
 1. A substrate processing system comprising: aradio frequency (RF) source configured to generate RF source energy in afirst frequency band to form a plasma within the system, wherein the RFsource is terminated through an electrode; a bias source coupled to theelectrode to apply bias energy to the electrode; a first filter disposedbetween the bias source and the electrode, the first filter configuredto pass the bias energy to the electrode, block RF source energy in thefirst frequency band from reaching the bias source and provide a lowimpedance to ground for the RF source energy in the first frequencyband; and an RF sensor disposed in serial with the first filter, whereinboth the RF sensor and the first filter that is configured to pass thebias energy to the electrode and provide the low impedance to ground forthe RF source energy in the first frequency band are disposed betweenthe electrode and the bias source, and the RF sensor is configured toprovide an indication of a voltage potential of the electrode.
 2. Thesubstrate processing system of claim 1, wherein the low impedance toground for the RF source energy in the first frequency band isconfigured as an RF short at the first frequency band of the RF sourceenergy.
 3. The substrate processing system of claim 1, wherein the firstfilter is a low pass filter.
 4. The substrate processing system of claim3, wherein the low pass filter comprises an inductor, a first capacitorand a second capacitor.
 5. The substrate processing system of claim 4,wherein the inductor has a value of approximately 4 microhenries, thefirst capacitor has a value of approximately 1200 picofarads and thesecond capacitor has a value of approximately 150 to 200 picofarads. 6.The substrate processing system of claim 1, wherein the first filter isa band pass filter.
 7. The substrate processing system of claim 1,wherein the RF source generates a first frequency and the bias sourcegenerates a second frequency that is different from the first frequency.8. The substrate processing system of claim 1, wherein the RF sourcegenerates a first frequency of approximately 13.56 MHz and the biassource generates a second frequency of approximately 400 kHz.
 9. Thesubstrate processing system of claim 1, wherein the RF sensor is housedwith the first filter.
 10. A substrate processing system comprising: asubstrate processing chamber; a substrate support positioned within andconfigured to be an electrode within the substrate processing chamber; aradio frequency (RF) source configured to generate RF source energy toform a plasma within the chamber from gases introduced into the chamber,wherein the RF source energy is coupled through the electrode andthrough a termination to ground; a bias source coupled to the electrodeto apply bias energy to the electrode; a filter disposed between theelectrode and the bias source, wherein the filter is configured to passthe bias energy to the electrode and to provide a low impedance toground for the RF source energy; and an RF sensor disposed in serialwith the filter, both the RF sensor and the filter disposed between theelectrode and the bias source, and the RF sensor configured toselectively measure voltage of one of the RF source energy or the biasenergy on the electrode.
 11. The substrate processing system accordingto claim 10, wherein the filter is configured to block the RF sourceenergy from reaching the bias source.
 12. The substrate processingsystem according to claim 10, wherein the termination to ground isconfigured to have a designed impedance at a frequency of the RF source.13. The substrate processing system according to claim 10, wherein thetermination to ground is configured as a short to ground at a frequencyof the RF source.
 14. The substrate processing system according to claim10, wherein the termination to ground is contained in a common housingwith the filter.